1. Field of the Invention
The present invention relates to a pressure measurement device with automatic position correction, and a method for determining pressure related thereto.
2. Background of the Invention
When pressure measurement devices are used to measure pressure, a so-called position error always results from the installation position of the pressure measurement device, said position error being incorporated as an error in the measurement of the pressure as a result of the orientation of the pressure measuring cell. This error arises as a result of the fact that, depending on the installation position, the weight of the measurement membrane itself, or—in the case of oil-submerged systems, the hydrostatic pressure of the oil in front of the measurement membrane as well—is measured together with the pressure being measured. In the case of ceramic capacitive measuring cells, this error—at 0.2 mbar, by way of example—is relatively small, but can significantly exceed the measurement precision of the device in cases where the measurement ranges are small—by way of example in the region of 100 mbar.
In the case of systems with a diaphragm seal, this error is generally larger. By way of example, an oil-submerged system can have a position error of up to several millibar depending on the distance of the diaphragm seal to the measuring element. The height of the oil column is the decisive factor in this case. As such, for an oil fill height of 5 cm, and an oil density of 0.8 g/cm3, a maximum position error is found by doubling the height of the filled oil, multiplied by the density of the oil and the acceleration due to gravity of 9.81 m/s2, giving a value of 7.8 mbar. The multiplication factor of 2 stems from the fact that if the measurement membrane is oriented facing the direction of the earth's gravity, the weight of the oil column on the measurement membrane creates pressure, whereas the measurement membrane oriented in the opposite measurement direction deflects the weight of the oil column in the opposite direction.
In general, all pressure measurement devices are calibrated in the installation position where the membrane faces downward toward the earth's gravity. However, installation at the customer site occurs in all possible installation positions, and only very rarely in the same installation position as the calibration. As a result, the customer must undertake a position correction manually. For this purpose, a corresponding operation function in the device, the same installed at zero pressure, must be carried out. In the process, the zero point is accordingly corrected. In the case of relative pressure devices, the device shows 0 mbar afterward. In the case of absolute pressure devices, it is not possible to correct the position so simply, because the device must be entirely evacuated for the position of the device to be corrected, or the exact ambient pressure must be known, and this can most often only be determined with a reference device. Both of these things are associated with a great additional expenditure of time and effort for the customer, or are in practice completely impossible from a technical perspective.
Therefore the problem addressed by the invention is that of providing pressure measurement devices which can automatically correct the position error.
This problem is addressed by a pressure transducer and a method for determining pressure, each as disclosed herein. Advantageous embodiments are disclosed in each of the dependent claims.